Field of Invention
The present disclosure relates to a circuit of light-emitting elements. More particularly, the present disclosure relates to a circuit in which light-emitting elements share a zigzag conducting line configured to be electrically connected to a power terminal.
Description of Related Art
In recent years, display devices have become one of the indispensable components of electronic products. In addition, owing to the exponential growth of network transmission rate and high coding efficiency of video compression technology, consumers have increasing demands for display quality.
Generally speaking, a backlight module of a display device usually enhances contrast ratio of the display device by light dimming. In greater detail, when the display device displays a dark picture (such as a night scene), the luminance of the backlight module is reduced. When the display device displays a bright picture (such as a sunny day), the luminance of the backlight module is increased. However, since the brightness across the picture is not constant, the backlight module performs a local dimming operation so as to satisfy the desired brightness at all pixels constituting the picture, thus improving contrast ratio of the display device.
Conventionally, in order to achieve local dimming, conducting states of light-emitting elements are controlled by adjusting a plurality of negative power terminals. FIG. 1 depicts a schematic diagram of a circuit of light-emitting elements 100. The circuit of light-emitting elements 100 comprises a plurality of light-emitting elements 101-106. First terminals of the light-emitting elements 101-106 are jointly in electrical connection with a positive power terminal. Second terminals of the light-emitting elements 101-106 are respectively in electrical connection with different negative power terminals. With respect to the driving method, the positive power terminal is maintained at a high voltage level, and local dimming function is implemented through adjusting voltage levels at the negative power terminals.
Although aforementioned method can achieve the objective of local dimming, paths starting from the positive power terminal, passing through each of the light-emitting elements 101-106, and ending at corresponding negative power terminals do not have identical length, given that a viewpoint following the current flow is taken into account. Moreover, the conducting line itself has a specific resistance value, that is, R=ρ(L/A), wherein R is the resistance value of the conducting line, L is the length of the conducting line, A is the cross-sectional area of the conducting line, and ρ is the resistivity of the conducting line. The magnitude of the resistivity ρ relates to the material property of the conducting line itself. Hence, the resistance values of paths passing through each of the light-emitting elements 101-106 are different. As a result, under the same driving voltage, the light-emitting intensities of the light-emitting element 101-106 differ from each other. For example, since the path in which the current flows through the light-emitting element 101 is much longer than the path in which the current flows through the light-emitting element 106, the luminance of the light-emitting element 101 is lower than the luminance of the light-emitting element 106, which makes the local dimming method inefficiently raise the contrast ratio of the display device. In addition, adjusting voltage levels at the plurality of negative power terminals also increases design complexity and power consumption of the external driving circuit.